When using three-phase motors for battery-operated floor conveyors a transformer is naturally required, which generates the three-phase alternating voltage from the battery voltage. The transformer conveniently contains three half-bridges, in each of which two semiconductor switches in the form of power transistors are disposed, for instance MOSFETs or also IGBT. The transformer has a power unit with power transistors for the generation of a three-phase output alternating voltage, a capacitor battery as a buffer capacity and a triggering electronics for the power transistors. Further, a control unit is provided which has a computing unit with appendant software. Power transistors as well as control units are conveniently disposed on one circuit mounting plate. The power transistors generate considerable heat, which has to be discharged onto the surroundings with the aid of corresponding cooling attachments or the like.
From DE 197 20 695 a transformer has become known, in which all the power transistors are arranged on a first current bar as parallel connected semiconductor branches of the three-phase bridge, and the power transistors of the respective other half-branch of the bridge are disposed on a separate current bar per phase, on which the respective phase voltage is picked up. The power transistors are in direct thermal contact with the current bars, which are part of a cooling attachment at the same time.
From DE 199 10 787 a transformer has become known, in which the cooling attachment is provided with three oblong portions disposed parallel in a distance, the transistors of each phase being attached alternately side by side in an insulated manner on one portion. Mounting plate portions are disposed in the two compartments between the cooling attachment portions, with which the transistors and the capacitors of the capacitor battery are connected, the mounting plate portion disposed in the wider compartment having two rows of transistors. Near to the rows of transistors an arrangement of three parallel current bars running in a distance is provided, respectively, of which a first current bar is provided for one phase, a second current bar for the minus potential and a third current bar for the plus potential.
The invention has as an objective to provide a driving system with converter control for three-phase motors, in which a high power density is obtained at relatively low manufacturing expenditure.